The invention relates to the porous textile product made from bioactive glass fiber, defined in claim 1. The invention further relates to the use of the said textile product.
The publications to which reference is made below and which are used for illustrating the background of the invention and the state of the art are to be deemed as being incorporated into the description of the invention below.
Biomaterials and their Biologic Attachment
Implants for both medical and dental purposes have long been prepared from a variety of materials. Various metals, metal alloys, plastics, ceramic materials, glass ceramic materials, and the latest, i.e. bioactive glasses, differ one from another not only by their durability but also by the properties of the interface between the implant and the tissue. Inert materials, such as metals and plastics, do not react with a tissue, in which case there always remains an interface between the implant and the tissue; the implant and the tissue constitute two distinct systems. Bioactive materials, such as hydroxyapatite, glass ceramic materials and bioactive glasses, react chemically with the tissue, whereupon there forms at the interface between the implant and the tissue a chemical bond, which is relatively strong, especially with bioactive glasses. The implant and the tissue are thus fixed to each other. The speed of the healing of the tissue and the possible chemical bond with the implant depend on the tissue activity of the implant material used.
International patent publication WO 96/21628, Brink et al., describes a group of bioactive glasses which can be processed easily. From such bioactive glasses it is possible, for example to draw fibers and, for example by the torch spraying technique, to prepare so-called microspheres of glass. Porous bioactive pieces are prepared by sintering these microspheres together. By using microspheres which are within as narrow a fraction as possible (of as uniform a size as possible), it is possible to control the porosity of the body. According to the literature it seems that the most advantageous particle size is within the fraction 200-400 microns (Schepers et al. 1997, Tsuruga et al. 1997, Schliephake et al. 1991, Higashi et al. 1996). The studies carried out by the inventors so far have shown that a porous bioactive implant which has been prepared by sintering bioactive microspheres of the fraction 250-300 microns reacts very strongly in the femur of a rabbit (Ylxc3xa4nen et al. 1997). The results of the studies have shown that the said implant model reacts rapidly and the porous matrix fills at a steady speed with new bone. The shear strength of the bioactive implants in a push-out to failure test has been already after three weeks statistically as high as after 12 weeks. The amount of bone inside the matrix has been after 12 weeks 35-40% of the pore volume both in bioactive implants and in the titanium implants used as controls. It is, however, advisable to note that in a bioactive matrix porosity increases evenly as a function of time as the bioactive glass mass decreases. Porosity increased in experiments in vivo from 30% to 65%. The porosity of titanium, of course., does not change in any way. Thus the amount of new bone inside bioactive implants is de facto almost double that inside titanium implants. In our opinion this shows that the porous implant type used by us is right.
The beginning of new bone growth seems to be located in micro-cracks in the bioactive glass particles (Schepers et al. 19967). Evidently the calcium and phosphate dissolving from the glass into the fluid (in vitro SBF, in vivo plasma) surrounding the micro-crack quickly form, together with the calcium and phosphate normally in the fluid, so high a concentration that the solubility product of the ions concerned is exceeded. As a consequence of this, calcium phosphate precipitates onto the silica gel on the surface of the bioactive glass and new bone growth begins. The porous body sintered from bioactive microspheres is full of microscopically small cavities. This explains the rapid bone growth inducing property of the tested bodies we sintered from bioactive microspheres. It has further been shown that the roughness of the surface has a favorable effect on the attachment to the biomaterial surface of proteins which control bone growth (Grossner et al. 1991, Boyan et al. 1998), as well as has the biomaterial itself. According to the literature, the said proteins attach best and most rapidly to the surface of bioactive glass (Ohgushi et al. 1993, Vrouwenvelder et al. 1992, Lobel et al. 1998, Vrouwenvelder et al. 1993, Shimizu et al. 1997, Miller et al. 1991).
Patent publication WO 98/47465 describes a porous composite which comprises i) particles A made from a bioactive material and ii) particles B which are made from a non-bioactive or weakly bioactive material sintrable to the said bioactive material. The said particles A and particles B are sintered together to form a porous composite. Combined with the implant, the said composite ensures both rapid ossification and permanent attachment of the implant. The composite described here, being made up of smooth glass spheres with untreated surfaces, must, however be in contact with body fluid for about a week before the silica gel layer required by bone growth is formed on the sphere surfaces. Only thereafter can the actual bone formation begin.
It is an object of the invention to provide a novel bioactive and porous textile product which ensures more rapid ossification than do prior art composites.
It is a particular object of the invention to provide a bioactive porous textile product having already, on the surface of its fibers, a bioactive layer required for the initiation of bone growth, in which case the integration of the bone to the composite can begin immediately after the composite comes into contact with body fluid, i.e. immediately after the surgery.
It is a further object of the invention to provide a bioactive porous product which is easy to mold and which, after the molding, can when necessary be hardened to the desired shape.
The characteristics of the invention are given in the independent claims.
The invention thus relates to a porous textile product made from bioactive glass fibers. It is characteristic that the fibers therein are of at least two kinds, fiber A and fiber B,
fiber A being made of a bioactive glass and
fiber B being made of a weakly bioactive glass.
The invention further relates to the use of the novel textile product as an implant, a product yielding a drug or some other substance at a controlled rate, for tissue control, as filler material in bone cavities or in soft tissue, for the removal of pulpa, as dental root filler material, or as binding material for bone transplants.